A number of Patent Publications on the technique of detection/removal of a mine have been applied not only in Japan but also in foreign countries, for instance References 1 to 4. However, not only the techniques described in the above-specified publications but also the techniques as described in many publications thus far published for detecting/removing a mine are detection methods for recognizing the mine as a foreign substance from the soil around it, in which the mine is buried, by employing an underground radar or a metal detector.
Publication 1: JP-A-2001-74387,
Publication 2: JP-A-2001-153597,
Publication 3: JP-A-06-506295, and
Publication 4: U.S. Pat. No. 6,411,208B1.
The mine detecting method thus far developed is roughly divided into two kinds. One is a method detecting the difference in physical properties between the mine and the soil around that, in which the mine is buried, and the other is a method for detecting the physical properties of the mine (or the explosive substance) itself directly.
The methods classified among the former include an electromagnetic induction method (metal detection), an electric wave method (dielectric rate), an electric survey method (specific resistance), a thermal survey method (heat capacity), an ultrasonic method (substance density), and so on. The methods classified among the latter include a nuclear magnetic resonance method (magnetic characteristics), a neutron method (radioactivation characteristics), a chemical method (bonding state of atoms), a biological method (with an antibody bio-film) and so on.
The nuclear magnetic resonance NMR method classified among the latter generally uses a nuclear magnetic resonance spectrometer, as is utilized at present in medical devices.
This NMR method, detecting a mine by means of the nuclear magnetic resonance, does not detect the differences in the physical properties such as the electric conductivity or the dielectric constant between the mine and the soil in which the mine is buried, as does the electromagnetic induction method (metal detector) or the electric wave method (underground radar). The NMR method directly detects the intrinsic nuclear magnetic field of the atoms composing the mine (or the explosive substance). The NMR method is accepted as excellent mine detecting means because it can detect the explosive substance of the detection target directly.
For the NMR method, however, a large-sized magnet is indispensable for generating an intense magnetic field. Thus, this NMR method utilizing nuclear magnetic resonance has a fatal defect when it is desired to reduce the size of the device. Therefore, the chemical substance detecting device according to the NMR method has been limited in practice to the MRI (Magnetic Resonance Imaging) for medical diagnosis, because the NMR method is viewed as not suited for a portable mine detecting device.
Therefore, the invention described in this application is presented to solve the problems identified in the prior art and to provide a mine detecting device, which is made so portable that it can be conveniently employed even outdoors.